1. Field of the Invention
The present invention relates to an optical communication system enabling bidirectional optical communication by using an optical signal having different wavelengths and an optical apparatus for use in optical communication using a computer-generated hologram (hereinafter referred simply as a xe2x80x9cCGH devicexe2x80x9d) that can be suitably embedded in the optical communication system.
2. Description of the Related Art
In recent years, in order to implement optical communication at a large communication capacity, a plan called a xe2x80x9cFiber to The Home (FTTH)xe2x80x9d to build an optical fiber in each home is in motion. The plan enables unidirectional optical communication achieved by transmission of light having a wavelength, for example, in a 1.55 xcexcm band from a base station to a home and reverse-directional optical communication achieved by transmission of light having a wavelength, for example, in a 1.31 xcexcm band from the home to the base station. Therefore, since light having different bands of wavelengths is transmitted in a reverse direction over an optical fiber path built between the base station and the home, each of the optical communication terminals on both the base station and home sides requires an optical apparatus for optical communication to multiplex or demultiplex optical signals having different wavelengths.
Since such the optical apparatus for use in optical communication is configured by using microoptic components including a microlens, optical demultiplexer or a like so as to be made smaller in size, it is necessary to assemble, with high accuracy, many optical parts. Because of this, the conventional optical apparatus for use in optical communication has a problem in that its manufacturing process is complicated and its manufacturing costs increase.
In view of the above, it is an object of the present invention to provide a novel optical apparatus for use in bidirectional optical communication and a novel optical communication system that can be easily manufactured at reduced costs and can be made compact.
According to a first aspect of the present invention, there is provided an optical apparatus for use in bidirectional optical communication including:
a common terminal used to receive diverging light with a long wavelength and to output light with a short wavelength which is shorter than the long wavelength;
an input terminal used to receive diverging light with the short wavelength from a light source;
an output terminal used to send out the diverging light with the long wavelength to a light receiver;
a wavelength selecting filter adapted to cause the light with the long wavelength transmitted from the common terminal to pass toward the light receiver and to reflect the light with the short wavelength transmitted from the input terminal to selectively direct the light to the common terminal;
first and second CGH devices used to guide the diverging light transmitted from the input terminal to the common terminal via the wavelength selecting filter and to cause the diverging light to converge to the common terminal, wherein the second CGH device causes the diverging light with the long wavelength transmitted from the common terminal to converge to the light receiver.
Thus, the present invention basically uses the CGH device based on an optical diffractive phenomenon as the optical element employed in the optical apparatus to implement bidirectional optical communication using light having different wavelength. By configuring above, it is possible to provide a fine CGH device with optical characteristics such as collimation function and light-gathering function as seen in the case of optical lens and with deflection function as seen in the case of a prism.
In the foregoing, a preferable mode is one wherein the first CGH device has a function of converting the diverging light with the short wavelength into a parallel luminous flux and of deflecting it, and wherein the second CGH device is optimized so as to deflect the parallel luminous flux converted from the light with the short wavelength toward the common terminal and to cause the parallel luminous flux to converge to the common terminal.
According to a second aspect of the present invention, there is provided an optical apparatus for use in bidirectional optical communication including:
a common terminal used to receive diverging light with a short wavelength and to output light with a long wavelength which is longer than the short wavelength;
an input terminal used to receive diverging light with the long wavelength from a light source;
an output terminal used to send out the diverging light with the short wavelength to a light receiver;
a wavelength selecting filter adapted to cause the light with the short wavelength transmitted from the common terminal to pass toward the output terminal and to reflect the light with the long wavelength transmitted from the input terminal to selectively direct the light to the common terminal;
first and second CGH devices used to guide the diverging light transmitted from the input terminal to the common terminal via the wavelength selecting filter and to cause the light to converge;
a third CGH device used to cause the light with the short wavelength transmitted from the common terminal through the second CGH device to converge to the output terminal.
In the foregoing, a preferable mode is one wherein the first CGH device has a function of converting the diverging light of the long wavelength into a parallel luminous flux and deflecting it, and wherein the second CGH device is optimized so as to deflect the parallel luminous flux converted from the light with the long wavelength toward the common terminal and to cause the light to converges and wherein the diverging light with the short wavelength transmitted from the common terminal, after having been dispersed by the second CGH device, is converged to the light receiver by the third CGH device.
According to a third aspect of the present invention, there is provided an optical communication system implementing bidirectional communication between a base station and a home and wherein the base station is provided with the optical apparatus stated in the second aspect and the home is provided with the optical apparatus stated in the first aspect and both of the common terminals of the optical apparatuses are connected through an optical fiber to each other.
The optical apparatus according to the present invention may include an optical block. The common terminal and the input terminal may be formed on one end of the block respectively and the output terminal may be formed on the other end of the block. The wavelength selecting filter may be mounted on or provided in the block.